The present invention relates to a low cost and practical tool control system and compilation of operational records of the stored program system numerical control equipment. Abrasion losses and cutting quality of bits used by machine tools are directly related to the resultant accuracy of finishing and surface roughness of the workpiece. Precise control of the condition of these tools is essential to the machining process. Theories, research, and measuring methods related to cutting conditions including life of tools, bit feed, spindle revolution, etc. have been published in many publications.
However, there have been considerable differences among the experimental data and the results of measurements. The technologies involved are complex and require high cost detectors or measuring instruments and, therefore, are not practical. Among other systems, the system with application of DNC (Direct Numerical Control) can be said to be the most practical. In this system, numerically controlled machine tools (to be called NC machine tools hereinafter) and the host computer for direct numerical control are on-line. On the host computer side, either the spindle-on-time is calculated as the first method, or the automatic operating time of the NC machine tool is calculated as the second method, and through these processes the working time of tools is calculated and controlled. As the third method, the spindle-on-time is calculated by attaching to the numerical control device an integrating indicator, which simply calculates spindle-on-time.
However, the first and third methods have shortcomings such as calculation of idle time and high cost of additional equipment. Even if the spindle is revolving, spindle revolution is not necessarily an indication of cutting operation since the operator may have halted automatic operation, inspecting the surface of the workpiece or cleaning the cutting area. The second method involves calculation of time which can be hardly termed as actual working time of a given tool. It involves calculation of idle time including the time for making preparations for the machining process such as locating time with a high speed feed and tool change time. If the objective is to control each tool, the data obtained through these methods cannot be used as they are, since, in effect, they represent operating time of the NC machine tool in operation or the spindle-on-time.
The fact that the equipment employed for these first, second, and third methods are complex and costly cannot be denied. Since the production control department must focus on cost reduction of products, it is of course very helpful to identify real working time of tools and operating time of NC machine tools under the current circumstances where development of tools is showing a remarkable progress.